In Situ Chemical Oxidation: Permanganate Oxidant Volume Design Considerations          下载免费PDF全文

Scott G. Huling  Randall R. Ross  Kimberly Meeker Prestbo 《Ground Water Monitoring & Remediation》2017,37(2):78-86

Contaminant rebound and low contaminant removal are reported more frequently with in situ chemical oxidation than other in situ technologies. Although there are multiple causes for these results, a critical analysis indicates that low oxidant volume delivery is a key issue. The volume of oxidant injected is critical and porosity of the aquifer matrix can be used to estimate the pore volume. The total porosity (q_T) is the volume of voids relative to the total volume of aquifer material. The mobile porosity (q_M) is the fraction of voids that readily contributes to fluid displacement, and is less than q_T leading to smaller estimates of oxidant volume. Injecting low‐oxidant volume may result in inadequate oxidant distribution and postinjection dispersal within the radius of influence, insufficient oxidant contact and oxidant loading, and incomplete treatment; whereas, greater oxidant volume achieves a greater oxidant footprint and may involve risk that the injected oxidant may migrate into nontarget areas and displacement of contaminated groundwater. Design guidelines and recommendations are provided that could help achieve more effective technology deployment, reduce the role of heterogeneities in the subsurface, and result in greater probability the oxidant is delivered to the targeted treatment zone.  相似文献   

Controls on the occurrence and prevalence of floodplain channels in meandering rivers          下载免费PDF全文

Scott R. David  Douglas A. Edmonds  Sally L. Letsinger 《地球表面变化过程与地形》2017,42(3):460-472

The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g. chute channels), but growing evidence suggests some channels originate outside of the channel‐belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3064 km² of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g. oxbow lakes) of chute‐channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down‐valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we compared the presence of channelization types with measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems are characterized by large floodplain‐to‐river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach‐scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo‐meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre‐existing topographic lows, such as meander cutoffs. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Evaluating carbon storage on subalpine lake deltas          下载免费PDF全文

Daniel N. Scott  Ellen E. Wohl 《地球表面变化过程与地形》2017,42(10):1472-1481

Mountainous regions are important contributors to the terrestrial organic carbon (OC) sink that affect global climate through the regulation of carbon‐based greenhouse gases. However, mountain OC dynamics are poorly quantified. We quantified OC storage in subalpine lake deltas in the Washington Central Cascades and Colorado Front Range with the objectives of determining the magnitude of transient carbon storage and understanding the differences in storage between the two ranges. We used field, laboratory, and GIS techniques to determine the magnitude of and controls on the subalpine lake delta OC pool in 26 subalpine lake deltas. Soil moisture, soil texture, mean basin slope, and delta valley confinement are significantly correlated with soil carbon on deltas. Average soil OC concentration on subalpine lake deltas ranges from 3 to 41%, and stocks range from 140 to 1256 Mg C/ha. Surprisingly, the carbon content of subalpine lake deltas is not significantly different between the two regions, despite stark contrasts in their climate, vegetation, and total ecosystem carbon stocks. We present a conceptual model that invokes geomorphic and biogeochemical processes to suggest that carbon is more likely to reach subalpine lake deltas from the upstream basin in the Colorado Front Range compared with the Washington Central Cascades, thus accounting for the similarity in OC storage between the two regions despite differences in total ecosystem carbon stocks and climate. This points to a complex interaction among carbon production, transport, and stability in each region, and supports the idea that geomorphic and biogeochemical processes determine the magnitude of transient OC storage more strongly than primary productivity or climate. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A catalogue of caldera unrest at Taupo Volcanic Centre,New Zealand,using the Volcanic Unrest Index (VUI)     

Sally H. Potter  Bradley J. Scott  Gill E Jolly  David M. Johnston  Vince E. Neall 《Bulletin of Volcanology》2015,77(9):1-28

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Water resources sustainability in a globalizing world: who uses the water?          下载免费PDF全文

Megan Konar  Tom P. Evans  Morgan Levy  Christopher A. Scott  Tara J. Troy  Charles J. Vörösmarty  Murugesu Sivapalan 《水文研究》2016,30(18):3330-3336

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On the origins of GEMS grains     

Lindsay P. Keller  Scott Messenger 《Geochimica et cosmochimica acta》2011,75(18):5336-5365

From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation.We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.  相似文献   

Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina     

Alyson Cartwright  Jay Quade  Scott Stine  Kenneth D. Adams  Wallace Broecker  Hai Cheng 《Quaternary Research》2011,76(3):430-440

Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38 m above modern lake level) lake persisted from no later than 28 ka to 19 ka, with the deepest lake phase from 27 to 22 ka. No evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17–10 ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM.  相似文献   

What kind of countryside do the public want: community visions from Wales UK?     

Alister J. Scott  James Shorten  Rosalind Owen  Iwan Owen 《GeoJournal》2011,76(4):417-436

This paper assesses how far community led rural visions accord with the current thrust of rural planning policy delivery in the UK. Adapting conventional visioning methods, qualitative techniques were used on eight different communities across urban, exurban and rural Wales to elicit views relating to the kind of local countryside(s) that were desired. The results show that the communities’ visions reflect an emerging consensus around local countryside priorities: multifunctionality, integration, wider countryside protection, development based on need, and local distinctiveness according with the thrust of current planning policy at national and local levels. However, there is a clear dichotomy between this and the reality of what communities actually experienced in developments affecting their countryside. Here, universal criticism was encountered over the type, pace and scale of development, the lack of rural specificity and the failure to take account of local community needs and priorities. It is hypothesized that tensions between national and local politics and stakeholder power relations are playing a crucial role in distorting the delivery of town and country planning. It is recommended that rural policy delivery must become more “joined up” and rural proofed at national and local levels concomitant with a change in the operational culture of agencies at the forefront of rural delivery. Essentially, effective engagement of top down approaches synergising with bottom up community led ideas is long overdue.  相似文献   

A spatially explicit degree-day model of Rift Valley fever transmission risk in the continental United States     

Sarah K. Konrad  Scott N. Miller  Will K. Reeves 《GeoJournal》2011,76(3):257-266

A spatially explicit degree-day model was used to evaluate the risk of Rift Valley fever virus (RVFV) transmission by mosquitoes to humans and livestock within five target states in the continental United States: California, Minnesota, Nebraska, New York, and Texas. A geographic information system was used to model potential virus transmission based on a 12-day moving window assessment of the extrinsic incubation period theorized for RVFV in the United States. Risk of potential virus transmission in each state was spatially evaluated on a 10-km grid using average historical daily temperature data from 1994 to 2003. The highest levels of transmission risk occur in California and Texas, with parts of these states at risk of RVFV transmission for up to 8 months per year. Northern Minnesota, central New York, and most of coastal and high-elevation California are at low to null risk. Risk of impact to the livestock industry is greatest in California, Texas, and Nebraska. A standard global climate model was used to evaluate future risk in the year 2030 in Nebraska, and showed an increase of transmission risk days from approximately 3 to 4 months per year.  相似文献   

Landscape response to tipping points in granite weathering: The case of stepped topography in the Southern Sierra Critical Zone Observatory     

Barbara S. Jessup  W. Jesse Hahm  Scott N. Miller  James W. Kirchner  Clifford S. Riebe 《Applied Geochemistry》2011

The dynamics of granitic landscapes are modulated by bimodal weathering, which produces patchy granular soils and expanses of bare rock ranging from meter-scale boulders to mountain-scale domes. We used terrain analysis and with cosmogenic nuclide measurements of erosion rates to quantitatively explore Wahrhaftig’s decades-old hypothesis for the development of “stepped topography” by differential weathering of bare and soil-mantled granite. According to Wahrhaftig’s hypothesis, bare granite weathers slower than soil-mantled granite; thus random erosional exposure of bare rock leads to an alternating sequence of steep, slowly weathering bedrock “steps” and gently sloped, but rapidly weathering, soil-mantled “treads.” Our investigation focused on the terrain surrounding the Southern Sierra Critical Zone Observatory (CZO), which is underlain by granitic bedrock and lies outside the limits of recent glaciation, in the heart of the stepped topography described by Wahrhaftig. Our digital terrain analysis confirms that steep steps often grade into gentle treads, consistent with Wahrhaftig’s hypothesis. However, we observe a mix-and-match of soil and bare rock on treads and steps, contrary to one of the hypothesis’ major underpinnings – that bare rock should be much more common on steps than on treads. Moreover, the data show that bare rock is not as common as expected at step tops; Wahrhaftig’s hypothesis dictates that step tops should act as slowly eroding base levels for the treads above them. The data indicate that, within each landscape class (i.e., the steps and treads), bare rock erodes more slowly than surrounding soil. This suggests that the coupling between soil production and denudation in granitic landscapes harbors a tipping point wherein erosion rates decrease when soils are stripped to bedrock. Although broadly consistent with the differential weathering invoked by Wahrhaftig, the data also show that steps are eroding faster than treads, undermining Wahrhaftig’s explanation for the origins of the steps. The revised interpretation proposed here is that the landscape evolves by back-wearing of steps in addition to differential erosion due to differences in weathering of bare and soil-mantled granite.  相似文献